Report Advisor: Dr. Vishwani D. Agrawal Report Committee: Dr. Shiwen Mao and Dr. Jitendra Tugnait Survey of Wireless Network-on-Chip Systems Master’s Project Defense Xi Li Department of Electrical and Computer Engineering Auburn University, AL USA Xi's M.E.E Presentation

Outline ※ Background ※ Problem Statement ※ General Solution ※ Contribution - Experimental Results and Analysis  Latency vs. Injection Rate  Latency vs. Number of Virtual Channels ※ Conclusion Xi's M.E.E Presentation

Background

※ Network-on-Chip (NoC) is an approach to designing the communication subsystem between IP cores on a single chip, modules are interconnected via switches (routers) ※ Size: mm-scale ※ Numbers of processors: dozens of or even hundreds of ※ Communication method:“Point-to-point” and “packet- based (usually in flit)” ※ Layered protocol (MAC layer, network layer) ※ Modules’ structures should be as simple as possible ※ Variety kinds of topologies are used in NoC Xi's M.E.E Presentation

A 4 by 4 regular mesh NoC topology

Problem Statement Xi's M.E.E Presentation

※ High latency and power consumption will be introduced due to 1) the multi-hop in the communication path between two nodes and 2) high injection rate. ※ More nodes in a chip, more hops and higher injection rate will be in the communication. Xi's M.E.E Presentation Many hops, high injection rate, and results a high latency

General Solutions Xi's M.E.E Presentation

※ Wireless link is introduced – reduce the number of hops in the path ※ Some outstanding transmission ways: UWB, mm-wave, CNT UWB-BasedMm-Wave-BasedCNT-Based Bandwidth3.6GHzTens of GHzAround 500GHz Devices’ sizesMillimeter order Micrometer order Transmission rangeNot enough (1mm)enoughEnough # of Channels per link multiplesinglemultiple Xi's M.E.E Presentation

※ Pure Wireless vs. Hybrid Wireless NoC system  Pure: All nodes are fully connected via wireless Limited wireless source Limited transmission range Therefore, hard to use in practice  Hybrid: Combination of wired and wireless Reduce the number of hop Alleviate latency Therefore, always used

※ Structure ※ Wireless insertion ※ Routing scheme and communication protocol Xi's M.E.E Presentation

※ Structure of Hybrid Wireless NoC system: Hierarchical  Bottom level: nodes form to a cluster via wired link  Top level: some clusters are connected by wireless (sometimes, clusters in neighbor are still connected by wired) Structure of hybrid wireless NoC

※ Wireless insertion: Using SA (simulated annealing) to get the optimal configuration – the placement of the wireless links ? Xi's M.E.E Presentation ? ? ?

※ Routing scheme and communication protocol  Should be as simple as possible  Routing schemes’ examples: Location-based (LBR), dimension-ordered, path length-based and some other adopting router scheme  Communication protocol: multi-channel protocol (combination of TDM and FDM)  Other used communication schemes: pulse position modulation, biphase modulation, on-off key modulation…

Contribution Contribution Xi's M.E.E Presentation

※ Experiment Xi's M.E.E Presentation  In this section, performance of both traditional NoC (wired) and wireless NoC will be simulated; then, a comparison between them will me make.  Some parameters: injection rate: bit/cycle per node latency: cycle virtual channel

※ Latency vs. Injection Rate (wired) ※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation 8 by 8 regular mesh:

※ Latency vs. Injection Rate (wired) ※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation  In order to reduce the distance between two nodes in wired communication, we can increase the concentration of the network.  Concentration stands for the number of nodes that share a single router. E.g. concentration 4 means a router is shared by 4 nodes.

※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation A 4 by 4 cmesh NoC topology

Xi's M.E.E Presentation A 4 by 4 regular mesh NoC topology

※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation  therefore, in cmesh topology, the average distance can reduce. 8 by 8 cmesh hop 8 by 8 regular mesh hop

※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation 8 by 8 cmesh:

※ Latency vs. Injection Rate (wired) Xi's M.E.E Presentation  However, since every router has more work to do, latency is still introduced  Therefore, there is a trade-off between the distance and number of nodes per router if we use wired link. Comparison between8 by 8 regular mesh and cmesh:

※ Latency vs. Injection Rate (wireless) Xi's M.E.E Presentation  Therefore, wireless NoC is needed  Here, we use a kind of topology to simulate wireless NoC system – flattened butterfly topology

※ Latency vs. Injection Rate (wireless) Xi's M.E.E Presentation A 4 by 4 flattened butterfly NoC topology

※ Latency vs. Injection Rate (wireless) Xi's M.E.E Presentation 64 nodes 256 nodes

※ Latency vs. Number of Virtual Channels (wired) Xi's M.E.E Presentation 8 by 8 regular mesh

※ Latency vs. Number of Virtual Channels (wireless) Xi's M.E.E Presentation Wireless NoC (64 nodes)

※ Comparison between wired and wireless Xi's M.E.E Presentation

Conclusion

 Comparison with traditional wired NoC, wireless NoC has a great improvement in performance (latency, maximum injection rate, so that the throughput)  In wireless NoC, before a specific level of injection rate, the latency increment is tiny.  Virtual channel plays a more important role in wireless NoC than in traditional NoC. ※ Conclusion

※ Future work Xi's M.E.E Presentation  Devices’ manufactory  Topology and communication protocol  Other aspect: fault tolerant and reconfiguration

Thank You Xi's M.E.E Presentation

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